How to achieve the cost-effective cutting edge quality for the PCD, PCBN knives?

The main reason to good quality lies in the choice of grinding wheel grain size.

The finer the particle size of the grinding wheel, the smaller the cutting edge chipping. But in the meanwhile, the fine the grain size of the grinding wheel, the lower the grinding efficiency will be.

That is why we should choose the right type of grinding wheel with proper particle size so that the PCD, PCBN knives grinding can achieve a good balance on efficiency and quality requirement.

Normally, we can divide the grinding into three stages: coarse, medium, and fine according to the accuracy.

Coarse-grained grinding wheels have a large contact area and high grinding force during grinding or sharpening(300-400N), which can remove excess machining allowance quickly.

Fine-grained grinding wheels have a small contact area and low grinding force during sharpening or grinding(100N-200N). And the grinding heat is low. But the material removal rate is also low.

The better way is to based on the roughness or the Ra that the PCD and PCBN knives require, and choose the right grit to achieve the balance of efficiency and Ra or accuracy.

The jumping of the grinding wheel should be ≤0.02mm

When the grinding wheel jumps too much, it will easily cause the cutting edge to chip, and it is difficult to obtain a high-precision cutting edge.

The grinding wheel should have a good dynamic balance.

Imbalance of the grinding wheel will affect the cutting edge quality and machining accuracy.

Vitrified bond diamond grinding wheels are the best solution for PCD, PCBN knives

For sharpening grinding wheels, vitrified bonded diamond grinding wheels should be preferred. Because the ceramic bond is prone to microcracks during the grinding process, the abrasive grains are renewed and self-sharpened, so that the grinding process is stable. The processed surface can be improved accurately and efficiently.

Resin-bonded grinding wheel can be also selected to grind the PCD and PCBN tools.

Sharpen the grinding wheel and choose the appropriate grain size of the sharpening stone

When processing PCD tools with diamond grinding wheels, the grinding wheels will be blocked, passivated. High temperature and rapid wear will result in reduced processing speed, vibration marks, noise and burns. 

So the sharpening dresser is needed. Usually, we choose soft silicon carbide stone as the sharpening stone and the particle grain will be 1 to 2 finer than that of the grinding wheel

For instance: the grinding wheel grit is 230/270#, the sharpening stone should be 325/400#;

Avoiding grinding metal and PCD at the same time

Since diamond is easy to chemically diffuse with iron-based alloys and accelerate the wear of the grinding wheel, it should be avoided as much as possible to grind metal and PCD at the same time;

The rotation direction of the grinding wheel must be rotated from the front face to the flank face

Rotation from the front face of the tool to the flank face, the cutting edge is not easy to chip or collapse. Otherwise, it is ensiled stress, and the cutting edge is easy to collapse. If it is necessary to reverse the grinding due to the tool structure, then the resin bond grinding wheel is better to choose than the metal bond or ceramic bond grinding wheels.

Using coarse-grained grinding wheel to grind the large relief angle, the fine-grained to the small relief angle

In order to ensure the quality of the cutting edge and improve the efficiency of the sharpening, the clearance angle of the tool can be two types: the large relief angle tool and the small relief angle tool.  Use a coarse-grained grinding wheel to grind the large relief angle first, because the contact area is large and the grinding force is large and the grinding efficiency is high. Then use a fine-grained grinding wheel to sharpen the small relief angle. The small relief angle should be controlled to about 0.1-0.3mm.

Complete the grinding in one clamping;

Every new lamping will differ, much time will be used to adjust the running of the grinding wheel;

Choose water-based coolant  rather than oil-based grinding fluid

PCD material has high hardness and poor heat resistance, the cooling effect of water-based grinding fluid is better than that of oil-based grinding fluid. Water-based coolants can improve processing efficiency and cutting edge quality.

Additionally, the cooling should be sufficient and continuous to avoid the large consumption of the diamond grinding wheel and the cutting edge damage of the tool due to the small amount of grinding fluid or the intermittent supply.